OBSERVATION OF RESONANT-TUNNELING BETWEEN MACROSCOPICALLY DISTINCT QUANTUM LEVELS

We report the first observation of resonant tunneling of a system betw een two macroscopically distinct states: energy levels in different fl uxoid wells of a weakly damped superconducting quantum interference de vice which differ in mean current by approximately 6 mu A. Near 50 mK, the tunneling rate Gamma(Phi(x)) from the metastable well vs applied flux Phi(x) is found to exhibit a series of local maxima where the lev els (spaced by approximate to 1.9 K) in the two wells cross. The posit ions of these maxima agree well with the level crossings calculated us ing independently determined system parameters.